Stirling cycle engine with power control by charge of working gas pressure

ABSTRACT

In a Stirling cycle engine, the power is controlled by manipulating a valve arrangement to connect one of a plurality of gas reservoir chambers containing working gas at different pressures to the working chamber.

United States Patent 1191 Giithberg Jan. 1, 1974 [5 STIRLING CYCLE ENGINE WITH POWER [58] Field of Search 60/24 CONTROL BY CHARGE OF WORKING GAS PRESSURE [56] References Cited [75] Inventor: Yngve Roland Giithberg, Malmo, UNITED STATES PATENTS Swede" 2,6l6,243 11 1952 Van Weenen 60/24 [73] Assignee: Kommanditbolaget United Stirling AB & a Primary Examiner-Martin P. Schwadron Sweden Assistant Examiner--Allen M. Ostrager [22] Filed: AP 12, 1972 Att0rney-Laurence R. Brown 21 A l. N 243 340 l 1 pp 0 57 ABSTRACT [30] Foreign Application Priority Data In a Stirling cycle engine, the power is controlled by manipulating a valve arrangement to connect one of a Apr. 24, 1971 Great Brita n l [,228/71 plurality of gas reservoir chambers containing working [52 11.5. C1 ..60/521 gas at d'fferem pressures the workmg chamber I 1 Int. Cl .."L.I.'.'I'.I. F02g l l04, F02g U06 5 Claims, 2 Drawing Figures STIRLING CYCLE ENGINE WITH POWER CONTROL BY CHARGE OF WORKING GAS PRESSURE This invention relates to a power-control device for a Stirling cycle hot gas engine.

It is known that the power of a Stirling cycle hot gas engine may be controlled in a very efficient way by adjusting the mean effective pressure of the working gas.

Hitherto such adjustment of the mean effective pressure has been effected by varying the quantity of working gas participating in the cycle, this quantity being reduced by pumping some of the gas out of the cycle into a high-pressure reservoir tank or increased by returning gas from this tank to the cycle. A short-circuiting or interconnection of the chambers at the two sides of the working piston of the engine may be used to bring the engine to a complete stop and may also be used for very quickly reducing the power output of the engine.

The present invention has for its object to provide a power-control device which does not need the provision of a separate compressor or pump but may still facilitate adjustments of the mean effective pressure of the working gas economically and rapidly.

According to the present invention there is provided a Stirling cycle hot gas engine characterized in that it comprises a plurality of reservoir chambers containing working gas and a valve system to allow selective connection of any one or more of said reservoir chambers with a space in the engine containing working gas at the maximum pressure which occurs during the cycle or with a space in the engine containing working gas at a lower pressure which occurs during the cycle.

The scope of the monopoly sought is defined in the claims hereinafter, and how the invention can be put into practice is described in more detail with reference to the accompanying drawing, in which:

FIG. 1 schematically shows a power-control device according to the invention, and

FIG. 2 is a graph to show variations in the working cycle pressure obtained by the control device of FIG.

In FIG. 1 the reference numerals l 7 designate seven bottles containing gas of the type used in the actual Stirling cycle hot gas engine, for example hydrogen or helium. The bottles are connected through a valve housing 8 to a conduit 9 which, through a valve 10, may be selectively connected either to a conduit 11 or to a conduit 12. The valve 10 may also selectively interconnect the conduits 11 and 12 or interrupt communication between the conduits 9, l1 and 12. The valve housing 8 contains means for connecting any one or more of the bottles 1 7 selectively to the conduit 9, depending on the working gas pressure in the engine.

The conduit 11 contains a non-return valve 13 allowing only flow through the conduit 11 in the direction from the valve 10 to the engine, thus causing the minimum cycle gas pressure to prevail in the conduit 11. The conduit 11 is connected to the low temperature compression chamber 14 of a cylinder 15 in a Stirling cycle hot gas engine. The cylinder 15 also comprises a high temperature expansion chamber 16, a displacer piston 17, a working piston 18, and a buffer space 19. The chamber 14 and the buffer space 19 are interconnected by a pipe 20 containing a non-return valve 21 allowing flow of gas only in the direction from the chamber 14 towards the buffer space 19, thus causing maximum cycle gas pressure to prevail in the buffer space 19.

The conduit 12 is connected to the buffer space 19 and thus also contains gas which is at the maximum cycle gas pressure.

FIG. 2 shows the pressure variations when the device shown in FIG. 1 is used, and at any one time only one bottle is connected to the buffer space 19 and the bottles are connected or disconnected successively in numerical sequence.

The ordinates of the diagram of FIG. 2 represent the gas pressures obtained during the Stirling cycle. The abscissae indicate the intervals during which the bottles are brought successively into use.

Initially we assume that the bottles Nos. 1 6 contain gas at different pressures, for example in bottle No. 6 at a pressure which may be found in FIG. 2 as the intersection I between a line designated min and the vertical line V at the left-hand end of the interval No. 6 having the same number as the respective bottle No. 6. These bottles Nos. 1 6 are shut off from the remainder of the power-control device.

Bottle No. 7 is connected to the conduit 9 through the valve 8, and the valve 10 connects said conduit 9 with the conduit 11. Thus the pressure in the bottle No. 7 is also at its minimum value the value found in FIG. 2 as the intersection K between the line min" and the vertical line at the left-hand end of the interval No.

The pressure of the gas in the Stirling cycle will vary between the lines min and max, following the heavy line indicated at the left-hand end of the interval No. 7.

It we now shut off the connection between the conduit 11 and the conduit 9, no change in the gas pressures in the Stirling cycle takes place.

We may now open the connection between the conduit 12 and the conduit 9 for a short period. During this period gas will flow from the buffer space 19 into the bottle No. 7. The pressure in the bottle No. 7 will rise, following the dotted line A in the diagram of FIG. 2. We now assume that the connection between the conduits 12 and 9 is shut off by the valve 10 as soon as the pressure in the bottle No. 7 has reached a value corresponding to the intersection between the dotted line A and the dash dotted vertical line in FIG. 2. The pressure in the Stirling cycle will now vary between min and max at the ends of the vertical dash dotted line. The mean effective pressure of the gas in the Stirling cycle has been decreased, and so has the power output of the engine.

We now open the connection between the conduits l2 and 9 and keep it open until the flow has ceased from the buffer space 19to the bottle No. 7. The rise in pressure in the bottle No. 7 will of course depend on the relative size of the volumes now interconnected. We assume that the volume of the bottle No. 7 is so large that the pressure in the bottle has reached the value corresponding to the intersection between the inclined dotted line A and the line max in FIG. 2.

The pressure of the working gas in the Stirling cycle will now vary along the heavy iertical line at the righthand end of interval No. 7 in FIG. 2.

In case a further decrease in mean effective pressure of the working gas in the Stirling cycle is desired, the connection between the bottle No. 6 and the conduit 9 is now opened.

Gas from the buffer space 19 is passed into the bottle No. 6 in the same way as described above regarding decreasing the power by passing gas from the buffer space to the bottle No. 7. In FIG. 2 the variations in the pressure of the gas in the Stirling cycle may be caused to range between the lines max and min following any vertical line within any of the intervals Nos. 7 1 inclusive.

It will be understood that decreases in the mean effective pressure of the working gas in the Stirling cycle are obtained by successively admitting gas into the bottles Nos. 7 1 in which initially the pressure corresponds to the value determined by the intersection of the line min" and the vertical line at the left-hand end of the correspondingly numbered interval in FIG. 2.

After thus admitting gas into the bottles the gas pressure in each bottle corresponds to the value determined by the intersection of the line max and the vertical line at the right-hand end of the correspondingly numbered interval in FIG. 2.

Let us now assume that the bottles Nos. 7 and 6 have been filled to the maximum pressure, and that it is now desired to increase the power output of the engine. The connection between the bottle No. 6 and the conduit 9 is open, whereas the connection between all other bottles and the conduit 9 is closed.

By opening the connection between the conduit 9 and the conduit 11 the latter conduit always containing gas at the minimum pressure which occurs in the Stirling cycle gas is now passed from the bottle No. 6 into the chamber 14 of the Stirling engine. The mean effective pressure of the gas in the Stirling cycle will now increase, while the pressure in the bottle No. 6 will decrease. The connection between the conduits 9 and 11 may be kept open until the pressure in the bottle N0. 6 has decreased to equal the minimum working gas pressure which occurs during the Stirling cycle. The said minimum pressure will of course increase in accordance with the amount of gas from the bottle reintroduced into the cycle.

When the flow of gas from the bottle No. 6 to the chamber 14 of the Stirling engine has ceased, the pressures of the gas in the cycle will vary along the heavy vertical line at the left-hand end of the interval No. 6 in F IG. 2. The connection between the bottle No. 6 and the conduit 9 is now closed, and the connection between the bottle No. 7 and the conduit 9 is opened and a further desired increase in the power output of the engine may now be obtained by keeping the connection between the conduits 9 and 11 open for a period long enough to produce the desired increase.

What is claimed is:

l. A power control apparatus for a Stirling cycle hot gas enging having a working gas supply therein comprising in combination, a plurality of sources of working gas for said engine each at a different pressure, and valve means selectively connecting different ones of said sources to the working gas supply in said engine wherein the engine has a first space containing working gas at the maximum pressure which occurs during the engine cycle, and a second space containing working gas at a lower pressure which occurs during the cycle, and wherein said valve means controls the connection of said sources to either of said spaces.

2. Apparatus as defined in claim 1 including a conduit connecting said spaces and a non-return valve in said conduit allowing flow of gas only from said first space to said second space.

3. Apparatus as defined in claim 1, wherein said first space comprises a compression chamber in said engine.

4. Apparatus as defined in claim 1, wherein said second space comprises a buffer space in said engine.

5. Apparatus as defined in claim 1, wherein the sources of working gas are gas bottle reservoir chambers. 

1. A power control apparatus for a Stirling cycle hot gas engine having a working gas supply therein comprising in combination, a plurality of sources of working gas for said engine each at a different pressure, and valve means selectively connecting different ones of said sources to the working gas supply in said engine wherein the engine has a first space containing working gas at the maximum pressure which occurs during the engine cycle, and a second space containing working gas at a lower pressure which occurs during the cycle, and wherein said valve means controls the connection of said sources to either of said spaces.
 2. Apparatus as defined in claim 1 including a conduit connecting said spaces and a non-return valve in said conduit allowing flow of gas only from said first space to said second space.
 3. Apparatus as defined in claim 1, wherein said first space comprises a compression chamber in said engine.
 4. Apparatus as defined in claim 1, wherein said second space comprises a buffer space in said engine.
 5. Apparatus as defined in claim 1, wherein the sources of working gas are gas bottle reservoir chambers. 